This invention relates to a navigation method and system for guiding a user through a calculated route to a destination, and more particularly, to a navigation method and system for accurately determining an optimum route to a destination where such a destination is within a large compound such as a shopping mall, an apartment complex, or the like.
A navigation system performs travel guidance for enabling a user to easily reach the selected destination. A typical example is a vehicle navigation system. The present invention is not limited to a vehicle navigation system but is applicable to other types of navigation system such as a PDA (Personal Data Assistant), a cellular phone, and other portable navigation devices. However, for the convenience of explanation, the following description is made mainly for the vehicle navigation system.
Such a navigation system detects the position of the vehicle, reads out map data pertaining to an area at the vehicle current position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc) or a HDD (hard disc drive), and displays a map image on a monitor screen (display) while superimposing a mark representing the current location of the vehicle on the map image. Alternatively, such map data can be provided to the vehicle from a remote server through a communication network such as Internet.
The vehicle position is determined by a self-contained navigation sensors (e.g. a distance traveled sensor and a bearing sensor) mounted in the vehicle or by a global positioning system (GPS) including an artificial satellite (satellite navigation) . The satellite enables absolute position detection and higher position accuracy than the self-contained navigation sensors. However, the satellite navigation involves problem of position detection failure such as in a tunnel or a building where the satellite radio signals are obstructed. Therefore, recent navigation systems utilize both self-contained navigation and satellite navigation to achieve improved performances.
As the present position of the vehicle changes with the travel of the vehicle, the vehicle current position mark in the map image on the screen is changed accordingly. Alternatively, the map is scrolled while the vehicle current position mark is fixed at a predetermined position, for example, at the center of the image. In either method, the navigation system enables the driver to recognize the map information of the area at the vehicle position at a glance.
When a destination is not set, such a navigation system functions as a locator map which indicates the current location of the vehicle on a map image. When the destination is set, the navigation system starts a route guidance function for setting a calculated route from the starting point to the destination. Typically, the route guidance function performs an intersection guidance process in which a monitor screen displays an enlarged intersection diagram and the direction in which the vehicle is to travel while displaying the guide route on a map. When a destination is input, a CPU in the navigation system determines a most suitable guided route from the current vehicle position to the destination and successively stores nodes (expressed in longitude and latitude) constituting the guided route in a memory.
During actual traveling, the node series stored in the memory is searched for a portion of the guided route to be displayed in a map display area of the monitor screen, and the portion of the guided route is highlighted so as to be discriminable from other routes. When the vehicle is within a predetermined distance of an intersection it is approaching, an intersection guidance diagram (an enlarged or highlighted intersection diagram with an arrow indicating the direction in which the vehicle is to turn at the intersection) is displayed to inform a driver of the desired one of roads or directions selectable at the intersection.
In the case where a destination is within a large compound such as a shopping mall or an apartment complex, an address of the destination in the typical map data represents an address number on a street facing the large compound. For example, FIG. 1 shows an example of layout of a shopping mall 20 having shops S1-S7 where a road A runs along the shopping mall 20. In the typical map data, an address of each shop is represented by an address number on the road A of a point defined by an imaginary line connecting between the road A and the shop.
Thus, in the map data, a shop S3 is represented, for example, by an address number at a point Y on the road A. Typically, the point Y is defined by an imaginary line L3 from the shop S3 which perpendicularly intersects with the road A. Similarly, in a navigation system, an address of a shop S6 is defined by an address number at a point X at which an imaginary line L6 from the shop S6 intersects perpendicularly with the road A and an address of a shop S7 is defined by an address number at a point Z at which an imaginary line L7 from the shop S7 intersects in perpendicular to the road A.
Therefore, when a user specifies the shop S6 in the navigation system as her destination, the navigation system calculates various routes to reach the point X on the road A and determines the best route to the point X. However, as shown in FIG. 1, if an entrance E of the shopping mall 20 is relatively far away from the point X, the route calculated by the navigation system may not the best route to the shop S6. In other words, there is a case in that the address of the shop S6 is significantly different from the actual entrance E of the shopping mall 20. In contrast, an address of a relatively small structure, such as a building B1 or B2 (address M or N on road B) will substantially match the physical entrance of the building.
Since a large shopping mall attracts many customers, a relatively large road runs in front of a shopping mall. Sometimes, in the map data used for a navigation system, a large road with center separators is considered two separate roads or two one-way roads (may also referred to as xe2x80x9cdivided roadxe2x80x9d). Such an example is shown in FIG. 2 where the road at the front of the shopping mall 20 is configured, in the map data, by a one-way road A1 and another one way road A2. In the situation of FIG. 2, the conventional navigation system may be programmed to allow vehicles only on the one-way road A2 (running toward the left) to enter the shopping mall 20.
Thus, a navigation system may guide the user to travel a route which is substantially longer than other route as shown in FIG. 3A. In the example of FIG. 3A, the navigation system may guide the user to take the one-way road A2 through a road D and road E (east bound), which is an unreasonable route having a much longer distance than a route (reasonable route shown by dotted line) taking a road C and road A1 (west bound). In reality, the reasonable route in FIG. 3A is available since, in many cases, the road A1 of FIG. 3A allows a vehicle to legally make a left turn or U-turn between the center separators.
However, sometimes, conventional navigation systems are not designed to include a U-turn in the guided route. Thus, the user has to take the unreasonable route of FIG. 3A to the destination. Alternatively, even though the navigation system is designed to include a U-turn in the guided route, it is designed so that such a U-turn can only be made at an intersection. Thus, in the example of FIG. 2, a vehicle running on the one-way road Al (west bound) has to make the U-turn at the intersection IS to take the one-way road A2 as shown in FIG. 3B. This route is unreasonable, since it involves a round-trip between the shopping mall and the intersection IS which is very long.
It may be possible to create, in advance, a special database which includes data indicating one-to-one relationships between shops and nearest entrances of the large compound. However, to create such a special database based on map data available in the market requires an extremely large amount of time and labor, resulting in cost increase of the navigation system. Therefore, as described in the foregoing, in the navigation system, there is a need of an effective way to determine the route to the destination when the destination is in the large compound.
It is, therefore, an object of the present invention to provide a navigation method and system for accurately determining a calculated route to a destination when the destination is in a large compound.
It is another object of the present invention to provide a navigation method and system for finding an entrance of a large compound as a target address rather than an assigned address of a destination without need of preparing a special database in advance indicating the one-to-one relationship between the destination and the entrance.
It is a further object of the present invention to provide a navigation method and system for finding an entrance of a large compound as a target address and a U-turn position to determine the best route to the target address.
The navigation method and system of the present invention is designed to search a link (entrance) to a large compound within a predetermined distance from an original address. When the link is found, the navigation system determines that the link as a target address and evaluates the possible route to the target address. The navigation method for guiding a user to the destination with use of map data is comprised of the steps of: examining an original address of the destination and judging whether the destination is within a large compound or not based upon the map data, searching for an entrance of the large compound from a road running along the large compound where the original address is on the road and the entrance is searched within a predetermined distance from the original address, defining the entrance of the large compound as a target address to the destination, and selecting a best route to the target address and starting a route guidance mode to guide the user to the entrance of the large compound.
In the process of judging whether the destination is within the large compound, the method of the present invention includes a step of evaluating the address of the destination as well as information on other POIs close to the destination. The process of searching for the entrance of the large compound includes a step of finding a link connecting the road and the large compound by evaluating the map data in backward and forward directions on the road. Further, the process of searching for the entrance of the large compound includes a step of specifying the predetermined search distance on the road from the original address.
The method of the present invention further comprises a step of finding a link connecting between two one-way roads when the map data defines that the road along the large compound as being constituted by the two one-way roads and selecting a best link for reaching the target address when two or more links exist for the road. This process further includes a step of finding a link allowing a U-turn from one one-way road to another one-way road and a step of selecting a link allowing the U-turn from one one-way road to another one-way road which is closest to the target address.
A further aspect of the present invention is a navigation system configured by various means for achieving the navigation method described above which finds the target address of the large compound based on the original address of the destination within the compound and determines the best route to the target address.
According to the present invention, the navigation method and system of the present invention is designed to search a link (entrance) to a large compound within a predetermined distance from an original address. When the link is found, the navigation system determines that the 10 link as a target address and evaluates the possible route to the target address. In the case where the road in front of the large compound is constituted by two one-way roads, the navigation method and system of the present invention searches for a link between the two one-way roads. The is navigation system also checks whether a link between the original address X and the target address E allows a U-turn of a vehicle. Thus, the navigation system is able to find the best route to the target address of the large compound including the U-turn from a one-way road to take another one-way road.